The scaling of integrated circuits has generated a demand for methods for forming nanometer-sized features that are separated by nanometer-sized distances. As the limits of optical resolution are approached in current lithography processes, double patterning processes have been used to provide for sub-lithographic feature size. Specifically, while a conventional lithographic process can be used to form a line-width equal to a minimum critical dimension (CD) associated with the lithographic process, a double patterning process can be used to form a line-width smaller than the CD. Double patterning techniques include “pitch split” (also called litho-etch litho-etch, or LELE) and “sidewall image transfer” (also called self-aligned double patterning or SADP). In each double patterning technique, a pattern that could not otherwise be printed is split into two separate masks.
To obtain even smaller feature sizes, litho-etch litho-etch litho-etch (LELELE) and Double SIT (or self-aligned quadruple patterning or SAQP) techniques have been proposed. These processes present overlay and cost issues. Further, while the Double SIT technique may shrink pitch to about 20 nanometers (nm), it requires two mandrel pulls that frequently result in residual materials within semiconductor structures. Such residual materials are challenging to remove with etching processes at reduced scaling. Further, the Double SIT technique is limited to ¼ and ⅛ scaling and has no flexibility for use with ⅓, ⅙ or 1/9 scaling.
Accordingly, it is desirable to provide methods for fabricating integrated circuits that provide for features having sub-lithographic dimensions. In addition, it is desirable to provide methods for fabricating integrated circuits that provide for a selected scaling, including ⅓, ⅙ or 1/9 scaling. Furthermore, other desirable features and characteristics will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and the foregoing technical field and background.